Baio first appeared onscreen in 1975 at age 13. He made guest appearances on series such as The Facts of Life, Fantasy Island and The Love Boat, but his best known role was probably as Billy Tate on the comedy series Soap (1977–81).
Baio's other credits include Matlock, Trapper John, M.D., Matt Houston, Too Close for Comfort and Family Feud. Baio, along with Susan Richardson, participated in the Junior Pyramid special of The $20,000 Pyramid in 1979. He also appeared in the comedy movie The Bad News Bears in Breaking Training (1977) as Carmen Ronzonni.